In FIG. 17, an example of circuit configuration of a first conventional power conversion device is shown. For the purpose of achieving a high-voltage output voltage to a motor connected to an output terminal, the power conversion device of FIG. 17 has a plural number of single-phase converters whose respective AC terminals are serially connected to each other. For the purpose of supplying power to the plural number of single-phase converters, a plurality of mutually-insulated DC power sources are formed by a transformer having plural windings and a plural number of diode rectifiers, and are connected to DC sections of the single-phase converters. Meanwhile, for the purpose of suppressing a harmonic current in the input side, the transformer is given as a transformer (phase-shifting transformer) including plural windings 3 to 11 whose phases are shifted to each other (see, for example, Patent Document 1).
On the other side, in FIG. 18, an example of circuit configuration of a second conventional power conversion device is shown. The power conversion device of FIG. 18 has a circuit configuration that is multiplexed using a plural number of three-phase converters having a common DC voltage and a plural number of three-phase transformers, in which secondary windings of the transformers are serially connected as open windings to each other (see, for example, Patent Document 2).
Furthermore, in FIG. 19, an example of circuit configuration of a third conventional power conversion device is shown. In the power conversion device of FIG. 19, each of single-phase transformers is connected at its primary side to other of the single-phase transformers in multi-serial fashion, and the serial ends are connected to input terminals, while a converter cell having a single-phase full-bridge converter/inverter that is configured, as shown in FIG. 20, with legs capable of outputting a two-level voltage, is connected to the secondary winding of each of the single-phase transformer. The AC output terminal of each inverter is connected to the AC output terminal of each other inverter in multi-serial fashion (see, for example, Patent Document 3).